U.S. patent number 5,244,039 [Application Number 07/786,035] was granted by the patent office on 1993-09-14 for rotary drill bits.
This patent grant is currently assigned to Camco Drilling Group Ltd.. Invention is credited to John M. Clegg, Thomas A. Newton, Jr..
United States Patent |
5,244,039 |
Newton, Jr. , et
al. |
September 14, 1993 |
Rotary drill bits
Abstract
A rotary drill bit for drilling holes in subsurface formations
comprises a bit body having a shank for connection to a drill
string, a plurality of preform primary cutting elements mounted on
the bit body and defining a primary cutting profile having a
downwardly convex nose portion. There are associated with at least
certain of the primary cutting elements respective secondary
elements which are spaced inwardly of the primary profile. The
distance of the secondary elements from the primary profile, when
measured in a direction perpendicular to said profile, is generally
greater for secondary elements nearer the nose portion than it is
for secondary elements further away from the nose portion, and is
preferably such that the vertical distance of the secondary
elements from the profile is substantially constant.
Inventors: |
Newton, Jr.; Thomas A. (Harris
County, TX), Clegg; John M. (Bristol, GB2) |
Assignee: |
Camco Drilling Group Ltd.
(Stonehouse, GB2)
|
Family
ID: |
25137405 |
Appl.
No.: |
07/786,035 |
Filed: |
October 31, 1991 |
Current U.S.
Class: |
175/431 |
Current CPC
Class: |
E21B
10/43 (20130101); E21B 10/602 (20130101); E21B
10/567 (20130101) |
Current International
Class: |
E21B
10/56 (20060101); E21B 10/00 (20060101); E21B
10/60 (20060101); E21B 10/42 (20060101); E21B
10/46 (20060101); E21B 010/46 () |
Field of
Search: |
;175/397,431,432,379,393,401 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Britts; Ramon S.
Assistant Examiner: Tsay; Frank S.
Claims
We claim:
1. A rotary drill bit for use in drilling or coring holes in
subsurface formations, comprising a bit body having a central
longitudinal axis and a shank for connection to a drill string, a
plurality of primary cutting elements mounted on the bit body and
defining a primary cutting profile having an angle of inclination
with respect to the central longitudinal axis of the bit body, and
having a nose portion, said angle of inclination decreasing in a
direction away from said nose portion, a passage in the bit body
for cooling and cleaning the cutting elements, at least some of the
primary cutting elements each comprising a preform cutting element
having a superhard front cutting face, there being associated with
and following with respect to the cutting direction at least
certain of said primary cutting elements respective secondary
elements spaced inwardly, with respect to said central axis, of
said primary profile, the distance of said secondary elements from
primary profile, when measured in a direction perpendicular to said
profile, being greater for secondary elements nearer the nose
portion than it is for secondary elements further away from the
nose portion.
2. A rotary drill bit according to claim 1, wherein the distance
from the primary profile of secondary elements furthest from the
nose portion is substantially zero.
3. A rotary drill bit according to claim 1, wherein a secondary
profile, defined by the secondary elements, is spaced inwardly of
the primary profile by a distance, measured perpendicular to the
primary profile, which decreases smoothly with distance from said
nose portion of the drill bit.
4. A rotary drill bit according to claim 1, wherein the distance of
a secondary profile, defined by the secondary elements, from the
primary profile is substantially constant, when measured in a
direction parallel to the longitudinal axis of the drill bit, over
at least a major portion of the primary profile.
5. A rotary drill Bit according to claim 1, wherein each secondary
element is spaced, rearwardly with respect to the normal direction
of rotation of the bit, from a respective cutting element.
6. A rotary drill bit according to claim 5, wherein each secondary
element is located at substantially the same radial distance from
the central longitudinal axis of the bit as the respective cutting
element.
7. A rotary element according to claim 1, wherein each preform
primary cutting element comprises a thin facing layer of superhard
material bonded to a less hard backing layer.
8. A rotary drill bit according to claim 1, wherein each cutting
element is mounted on a carrier received in a socket in the bit
body.
9. A rotary drill bit according to claim 1, wherein each secondary
element comprises a stud-like element protruding from the bit
body.
10. A rotary drill bit according to claim 9, wherein the stud-like
element is separately formed from the bit body and has one end
received and retained within a socket in the bit body, the other
end the stud-like element protruding from the bit body.
11. A rotary drill bit according to claim 9, wherein the stud-like
element is integral with the bit body.
12. A rotary drill bit according to claim 6, wherein a single body
of superhard material is embedded in said projecting end of the
stud-like secondary element.
13. A rotary drill according to claim 12, wherein the projecting
end of the stud-like secondary element is generally frusto-conical
in shape, and said single body of superhard material is embedded at
the central extremity of said frusto-conical shape.
14. A rotary drill bit according to claim 10, wherein a plurality
of bodies of superhard material are embedded in at least the
projecting end of said stud-like element.
15. A rotary drill bit according to claim 10, wherein said
stud-like secondary element is formed from tungsten carbide.
16. A rotary drill bit according to claim 1, wherein the primary
cutting elements and secondary elements are located on the bit body
in radially spaced groups, the distance between the primary profile
and secondary profile defined by the secondary elements, measured
perpendicular to the primary profile, being substantially uniform
within each group but decreasing from group to group as the
distance of the group from the nose portion of the bit
increases.
17. A rotary drill bit for use in drilling or coring holes in
subsurface formations, comprising a bit body having a central
longitudinal axis and a shank for connection to a drill string, a
plurality of primary cutting elements mounted on the bit body ad
defining a primary cutting profile having an angle of inclination
with respect to the central longitudinal axis of the bit body, and
having a nose portion, said angle of inclination decreasing in a
direction away from said nose portion, a passage in the bit body
for supplying drilling fluid to the surface of the bit body for
cooling and cleaning the cutting elements, at least some of the
primary cutting elements each comprising a preform cutting element
having a superhard front cutting face, there being associated with
and following with respect to the cutting direction at least
certain of said primary cutting elements respective secondary
elements spaced inwardly, with respect to said central axis of said
primary profile, the distance of said secondary elements from the
primary profile, when measured in a direction perpendicular to said
profile, varying in accordance with said angle of inclination, said
distance decreasing as said angle of inclination approaches
zero.
18. A rotary drill bit according to claim 13, wherein the distance
of a secondary profile, defined by said secondary elements, from
the primary profile is substantially constant, when measured in a
direction parallel to the longitudinal axis of the drill bit .
Description
BACKGROUND OF THE INVENTION
The invention relates to rotary drill bits for use in drilling or
coring holes in subsurface formations, and of the kind comprising a
bit body having a shank for connection to a drill string, a
plurality of cutting elements mounted on the bit body, and a
passage in the bit body for supplying drilling fluid to the surface
of the bit body for cooling and/or cleaning the cutting elements,
at least some of the cutting elements each comprising a preform
cutting element having a superhard front cutting face.
The invention is particularly, but not exclusively, applicable to
drill bits of the kind in which the cutting elements comprise
preforms having a thin facing layer of polycrystalline diamond
bonded to a backing layer of tungsten carbide. Such bits and
cutting elements are well known and will not therefore be described
in detail.
When drilling deep holes in subsurface formations, it often occurs
that the drill bit passes through a comparatively soft formation
and then strikes a significantly harder formation. Also there may
be hard occlusions within a generally soft formation. When a bit
using preform cutters meets such a hard formation the cutting
elements may be subjected to very rapid wear or damage.
It has therefore been proposed to provide, on the rearward side of
at least certain of the preform cutting elements, which may be
regarded as primary cutting elements, secondary abrasion elements
which are set slightly below (or inwardly of) the primary cutting
profile defined by the primary cutting elements.
In this specification, the primary cutting profile is defined to
mean a generally smooth notional surface which is swept out by the
cutting edges of the primary cutting elements as the bit rotates
without axial movement. The secondary profile is similarly defined
as the notional surface swept out by the secondary elements.
With such an arrangement, during normal operation of the drill bit
the major portion of the cutting or abrading action of the bit is
performed by the preform primary cutting elements in the normal
manner. However, should a primary cutting element wear rapidly or
fracture, so as to be rendered ineffective, for example by striking
a harder formation, the associated secondary abrasion element takes
over the abrading action of the cutting element, thus permitting
continued use of the drill bit. Provided the primary cutting
element has not fractured or failed completely, it may resume some
cutting or abrading action when the drill bit passes once more into
softer formation.
The secondary elements may be formed in a variety of ways. For
example, U.S. Pat. Nos. 4,718,505 and 4,889,017 describe a
secondary abrasion element comprising a plurality of particles of
superhard material, such as natural diamond, embedded in an
elongate stud-like carrier element having one end wholly enclosed
within a socket in the bit body which is spaced rearwardly from the
respective primary cutting elements, and the other end protruding
freely from the bit body transverse to the normal direction of
rotation of the bit.
Hitherto, it has been the usual practice for all the secondary
elements to be set slightly below, or inwardly of, the primary
cutting profile by a substantially constant distance, measured
perpendicular to the primary profile. However, it is believed that
this may be disadvantageous, and may have the effect that secondary
elements on some parts of the bit come into operation before
secondary elements on other parts, even though they may be
subjected to the same local conditions.
Because the drill bit is moving axially as drilling proceeds, the
parameter which determines when a secondary element comes into
operation, other things being equal, is its position, relative to
the primary profile, measured in a direction parallel to the
longitudinal axis of rotation of the drill bit (referred to herein,
for convenience, as the "vertical" distance). However, the primary
cutting profile of the drill bit is usually shaped to provide a
"nose" portion which is generally convex, although not necessarily
smoothly curved, when viewed in cross-section. The nose portion of
the profile is that part thereof which is lowermost when drilling
vertically. The nose portion may lie on the central longitudinal
axis of the bit in the case where the primary profile is simply
convex, or it may comprise an annular area spaced outwardly of said
axis in the case where the central portion of the profile is
concave, cone-shaped, or otherwise re-entrant.
Due to the generally convex shape of the nose portion, as viewed in
cross-section, the vertical distance between each secondary element
and the primary profile increases with distance from the nose
portion of the profile if the secondary elements are spaced by a
constant distance from the profile, measured perpendicularly from
the profile.
This means that, when harder formation or occlusions are
encountered when drilling, the backing-up or depth stop function is
not shared equally between the secondary elements, but falls mainly
on the secondary elements nearer the central axis of the bit,
leading to excessive wear and/or failure of those elements.
The present invention therefore sets out to provide an improved
form of drill bit in which this disadvantage may be alleviated or
overcome.
SUMMARY OF THE INVENTION
According to the invention there is provided a rotary drill bit for
use in drilling or coring holes in subsurface formations,
comprising a bit body having a central longitudinal axis and a
shank for connection to a drill string, a plurality of primary
cutting elements mounted on the bit body and defining a primary
cutting profile having a nose portion, a passage in the bit body
for supplying drilling fluid to the surface of the bit body for
cooling and/or cleaning the cutting elements, at least some of the
primary cutting elements each comprising a preform cutting element
having a superhard front cutting face, there being associated with
at least certain of said primary cutting elements respective
secondary elements spaced inwardly of said primary profile, the
distance of said secondary elements from the primary profile, when
measured in a direction perpendicular to said profile, being
generally greater for secondary elements nearer the nose portion
than it is for secondary elements further away from the nose
portion.
It will be appreciated that, if the spacing between a secondary
element and the profile defined by the primary cutters is
increased, the time at which that secondary element comes into
operation during use of the drill bit will be effectively delayed.
By adjusting the distance by which each secondary element is spaced
from the primary cutting profile in accordance with the invention,
it is possible to ensure that secondary elements on different parts
of the bit body come into operation at substantially the same time
regardless of their location of the bit and even though their
respective cutting elements may be subjected to different rates of
wear.
The distance from the primary profile of secondary elements
furthest from the nose portion may be substantially zero.
Preferably the secondary profile, defined by the secondary
elements, is spaced inwardly of the primary profile by a distance,
measured perpendicular to the primary profile, which decreases
smoothly with distance from said nose portion of the drill bit.
Preferably also, the distance of at least the majority of said
secondary elements from the primary profile is substantially
constant, when measured in a direction parallel to the longitudinal
axis of the drill bit. That is to say the distance between the
profiles is substantially constant, when measured in a direction
parallel to the longitudinal axis of the drill bit, over at least a
major portion of the primary profile.
In one embodiment, each secondary element is spaced, rearwardly
with respect to the normal direction of rotation of the bit, from a
respective cutting element. Advantageously, each secondary element
is located at substantially the same radial distance from the
central longitudinal axis of the bit as the respective cutting
element. It will be appreciated that, in this case, if the two
profiles are uniformly vertically spaced then the vertical distance
between each cutter and its associated abrasion element will also
be uniform.
Conveniently, each preform primary cutting element comprises a thin
facing layer of superhard material bonded to a less hard backing
layer, and each cutting element may be mounted on a carrier
received in a socket in the bit body.
Preferably each secondary element comprises a stud-like element
protruding from the bit body. The stud-like element may be
separately formed from the bit body and have one end received and
retained within a socket in the bit body, the other end of the
stud-like element protruding from the bit body. Alternatively the
stud-like element may be integral with the bit body.
In either arrangement a single body of superhard material may be
embedded in said projecting end of the stud-like secondary element.
For example, the projecting end of the stud-like secondary element
may be generally frusto-conical in shape, said single body of
superhard material being embedded at the central extremity of said
frusto-conical shape.
Alternatively a plurality of bodies of superhard material may be
embedded in at least the projecting end of said stud-like
element.
In another embodiment said stud-like secondary element may be
formed from tungsten carbide.
The primary cutting elements and secondary elements may be located
on the bit body in radially spaced groups, the distance between the
primary profile and the secondary profile being substantially
uniform within each group but decreasing from group to group as the
distance of the group from the nose portion of the bit
increases.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of the end face of a rotary drill bit
including primary cutting elements and secondary abrasion
elements;
FIG. 2 is a diagrammatic section through one primary cutting
element and its associated secondary abrasion element;
FIG. 3 is a diagrammatic half-section through a rotary drill bit
according to the invention, showing both primary cutting elements
and secondary abrasion elements; and
FIG. 4 is a similar view to FIG. 3 showing a further embodiment of
the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to FIG. 1: a rotary bit body has a leading end face 10
formed with a plurality of blades 12 upstanding from the surface of
the bit body. Drilling fluid is supplied through a passage (not
shown) within the bit body, and flows out through nozzles 14
located on the leading face 10 so as to cool and clean primary
cutting elements 16 mounted side-by-side along each blade 12.
Spaced rearwardly of the outermost cutting elements 16 on each
blade are secondary abrasion elements 18. Although the drawing
shows only two abrasion elements 18 mounted on each blade 12, any
number of the primary cutting elements 16 may be provided with an
associated abrasion element 18, and although each abrasion element
18 may lie at the same radial distance from the axis of rotation of
the bit as its associated cutting element 16, this is not
essential.
The secondary abrasion elements 18 shown in FIG. 1 each comprise a
single body of superhard material, such as natural or synthetic
diamond, mounted at the apex of a generally conical end face of a
stud, for example of cemented tungsten carbide, received in a
socket in the blade 12. However, other forms of secondary element
may be employed. For example, the separate stud may be replaced by
a projecting boss, formed integrally with the bit body and in the
conical extremity of which the superhard element is embedded.
FIG. 2 shows in greater detail another suitable form of secondary
abrasion element, which will be described below. Although the
secondary elements specifically described are abrasion elements,
the invention also includes arrangements where the secondary
elements are cutting elements, for example are similar to the
primary elements and comprise polycrystalline diamond preform
cutting elements.
As previously mentioned, in an alternative embodiment the secondary
elements may be in the form of tungsten carbide studs protruding
from the bit body. The studs may be integral with the bit body,
forming bosses on the surface thereof, or may comprise separately
formed studs which are received and retained in sockets in the bit
body.
Referring to FIG. 2, each primary cutting element 16 is a circular
preform comprising a front thin hard facing layer 20 of
polycrystalline diamond bonded to a thicker backing layer 22 of
less hard material, such as tungsten carbide. The preform is
bonded, in known manner, to an inclined surface on a generally
cylindrical stud 24 which is received in a socket in the bit body
10. The stud 24 may be formed from cemented tungsten carbide. The
bit body 10 may be machined from steel or may be moulded from
matrix material by a powder metallurgy process, in known
manner.
Each secondary abrasion element 18 also comprises a generally
cylindrical stud 26 which is received in a socket in the bit body
10 spaced rearwardly of the stud 24. In this example the stud 26 is
formed from cemented tungsten carbide impregnated with particles 28
of natural or synthetic diamond or other superhard material. The
superhard material may be impregnated throughout the body of the
stud 26, or may be embedded in only the outer surface portion
thereof.
In the arrangement shown, the stud 26 of the abrasion element
extends substantially at right angles to the surface of the
formation 32, but operation in softer formations may be enhanced by
inclining the axis of the stud 26 forwardly or by inclining the
outer surface of the abrasion element away from the formation in
the direction of rotation.
In order to improve the cooling of the cutting elements and
abrasion elements, a channel for directing drilling fluid may be
provided between the two rows of elements as indicated at 30 in
FIG. 2.
Any known form of preform cutting element 16 having a superhard
cutting face may be employed and the invention includes within its
scope arrangements where the cutting element is mounted directly on
the bit body, or on another form of support in the bit body, rather
than on a cylindrical stud such as 24.
It will be seen that the primary cutting element 16 projects
downwardly slightly further than the associated abrasion element
18, so that initially, before any significant wear of the cutting
element has occurred, only the cutting element 16 engages the
formation 32. The abrasion element 18 will only engage and abrade
the formation 32 when the primary cutting element 16 has worn
beyond a certain level, or has failed through fracture. The further
the cutting element 16 projects downwardly below the abrasion
element 18 the greater is the wear of the primary element which
must occur before the abrasion element 18 begins to abrade the
formation 32. It is therefore possible, by selectively varying the
vertical distances between the primary cutting elements 16 and the
abrasion elements 18, to ensure that each of the abrasion elements
18 comes into operation and begins to abrade the formation 32 at
substantially the same point in time during operation of the drill
bit, and FIGS. 3 and 4 show two particular arrangements of cutting
elements and abrasion elements by which this result may be
achieved, in accordance with the present invention.
FIG. 3 is a diagrammatic sectional representation of one half of a
rotary drill bit having a generally cone-shaped central recess 34
and a gauge portion 36. The central longitudinal axis of rotation
of the drill bit is shown by the dotted line 38. A row of primary
cutting elements 16 and associated secondary abrasion elements 18
is shown extending from the central recess 34 to the gauge portion
36. Each abrasion element lies directly behind its respective
cutting element, with respect to the normal direction of forward
rotation of the drill bit.
FIGS. 3 and 4 are intended to show, in a single quasi-sectional
view, the relative radial positions of a series of primary and
secondary elements on the drill bit. Although all the elements of a
given type (i.e. primary or secondary) may be arranged side-by-side
along a single blade, as shown, they could equally well be spaced
apart circumferentially as well as radially, on the bit body. FIGS.
3 and 4 should therefore be regarded as representing the radial
positions in which a series of circumferentially spaced elements
pass through a fixed transverse plane, once during each revolution
of the bit. Whereas the bit shown in FIG. 1 only has abrasion
elements trailing the outermost cutting elements, the bit
represented by FIG. 3 has abrasion elements spanning virtually the
entire bit face.
In practice also, the bit body will normally carry further cutting
elements, not shown in FIGS. 3 and 4, the radial positions of which
further elements overlap the radial positions of the elements
shown, so that a substantially continuous surface profile is cut in
the formation as the drill bit rotates.
The profiles defined by the primary cutting elements and the
secondary abrasion elements are represented by dotted lines 40 and
42 respectively.
Due to the presence of the central cone-shaped recess 34 in the bit
body, each of the primary profile 40 is generally convex as seen in
section, so as to provide an annular nose portion 46 which is
lowermost when the drill bit is drilling vertically downwards.
It will be seen that, in the arrangement of FIG. 3, the spacing
between the profiles of the cutting and abrasion elements 40, 42,
(measured perpendicularly to the primary profile 40) decreases
continuously as the profiles extend away from the annular nose
portion 46. The rate of decrease is such as to maintain a
substantially uniform vertical distance (i.e. measured in a
direction parallel to the axis 38) between the two profiles in the
region between the nose portion 46 and the outermost cutting
elements 43.
The spacing between the profiles 40, 42 decreases to zero in the
region of the gauge portion 36. In the arrangement shown, the
decrease in the spacing between the profiles is more rapid radially
inwards of the nose portion, and becomes substantially zero at the
location of the innermost element 41. In other embodiments of the
invention, however, a fixed vertical spacing between the two
profiles may be maintained also in the central recessed region
34.
In the variant of FIG. 4 the cutting elements 16 and associated
abrasion elements 18 are arranged in radially spaced groups, as
denoted by dotted separation lines 44. The spacing between the
abrasion elements 18 and the primary profile 40 of the cutting
element (measured perpendicular to the profile) is uniform within
each group, but the spacing for successive groups decreases as the
distance of the group from the nose portion 46 increases.
* * * * *